1. Field of the Invention
The present invention relates to a telecommunications network system for communicating between different versions of Internet protocol (IP), and more particularly to a telecommunications network system with multiple translators for converting IP packets between different IP versions.
2. Description of the Background Art
Conventional types of telecommunications network system communicating between different IP versions include one in which an IP Version 4 (IPv4) terminal connectable to an IPv4 server-over an IP Version 6 (IPv6) network. Such a conventional type of telecommunications network system accomplishes-packet transfer by means of, so-called Ipv4-in-IPv6 tunnel connection, which could be called capsuling. The tunnel connection is generally used in access networks for connecting user terminals to an Internet service provider (ISP) network.
In such a conventional type of telecommunications network system, an access network owns a broadband access server (BAS) serving as an IPv4 server, which is connected to ISP networks functioning under IPv4 protocol. Providers in an ISP network provide users with services specific to the network. The broadband access server also includes a subscriber management database, which stores subscriber identifications (IDs) for identifying users and global IP addresses for IPv4 (Gr-v4) corresponding to IPv4 user terminals so as to manage the users, or subscribers, enjoying the services. The broadband access server is also allotted to a global IP address for IPv6 (Gr-v6) for use in connection to the IPv6 access network.
For example, IPv4 user terminals subscribing to IPv4 ISPs different from each other may be connected to an IPv6 access network by means of a network terminal unit (NTU) which is assigned to a Gr-v4 address by the ISP network. Those IPv4 terminals are assigned to private IP addresses for IPv4 (Pr-v4) specific to the terminals. The network terminal units are adapted to convert a Pr-v4 address obtained from an IPv4 terminal connected thereto to a Gr-v4 address for connection to the IPv6 access network to thereby establish a tunnel connection over the IPv6 access network to the broadband access server. More specifically, the Pr-v4 address of an IPv4 terminal is converted to the Gr-v4 address of the network terminal unit, and the Gr-v4 address thus converted is capsuled into a Gr-v6 address, and then tunneled.
In the conventional type of telecommunications network system, however, the user terminals are connected to the ISP network, thus causing capsuling to decrease the effective transfer bandwidth. The capsuling, which adds headers to packets, may cause the packets to exceed the maximum transmission unit (MTU), thus causing fragments, so that the data transfer efficiency of the network is degraded.
Some conventional type of telecommunications network systems similar to what was described above for connecting an IPv4 terminal to an IPv4 terminal over an IPv6 access network, may include network application translators (NATs) provided in a level higher than respective IPv4 ISP networks. In such a type of network system, each network terminal unit has its Pr-v4 address assigned by the ISP network. A tunnel connection is accomplished by converting the Pr-v4 address of an IPv4 terminal to the Pr-v4 address of the network terminal unit, which is in turn capsuled into the Gr-v6 address, which will then be tunneled. The function of the network application translators can support the IPv4 terminals to which only Pr-v4 addresses are assigned by means of the Gr-v4 address which the translators own, thus saving the resources of Gr-v4 addresses. That type of network system also includes a subscriber management database which stores subscriber IDs to identify users and the Pr-v4 addresses of IPv4 terminals corresponding to the users.
In that type of telecommunications network system, the function of the network application units executes an application level gateway (ALG) process of converting the address stored in the payload of packets, e.g. from an IPv4 to an IPv6 address. The load of the ALG processing also degrades the transfer efficiency of the network.